Process of muffling lithopone and apparatus therefor



mii 8, 1924 H. G. SCHANCHE PROCSS OF MUFFLING LITHOPONE AND APPARATUS THEREFOR FiledA May l1 1921 v/ nO Fly.;

. Patented Apu-o g? m24 carica- HERMAN' G. SCHANCHE, OF PHILADELPHIA., PENNSYLVANIA, ASSIGNOR TO E. I. DU PONT DE NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE.

PROCESS OF MUFFLING LITHOPONE AND APPARATUS THEREEOR Application led May 11, 1921.

T o all Iwiz/m t may concern.

Be it known that I, HERMAN G. Sorian- CHE, a citizen of the United States, and a resident of Philadelphia, in the county of Philadelphia and State of Pennsylvania,

have invented a' certain new and useful Process of Muiiiing Lithopone and Apparatus Therefor, of which the following is a specification.

This invention relates to the manufacture of lithopone and more particularly it relates to a proc-ess of muiiling lithopone and to apparatus wherewith such process may be readily and conveniently carried out.

In the manufacture of lithopone, one of the important steps is the calcination of the pigment. rlhe precipitated mixture of zinc sulphide and barium sulphate, ordinarily known as raw lithopone, is filtered and at least partiallv dried, and then heated until it is perceptibly red (the color first appears belowO()o C.). After the proper temperature has been reached the pigment is quenched in water. By the calcination the tinting strength of the pigment is increased and the oil absorption is decreased. At intervals during the above mentioned calcination the lithopone is customarily stirred or rabbled with rakes operated by hand; this operation is not only burdensome, but makes it difiicult to avoid excessive oxidation of the lithopone by air. which gains entrance while the stirring is being performed. l have devised a process and apparatus for calcining litho e5 pone whereby these objections may be overcome, and a high grade lithopone obtained.

ln brief, the invention consists :in-calciuing the lithopone while preventing access of air thereto at any time during the calcina- 4o tion, and in apparatus therefor. By working in accordance with the invention, excessive oxidation of the pigment during calcination is eliminated and pigment of desired character is readily produced.

Some of the literature on lithopone, of course, refers to calcination in sealed retorts or with exclusion of air, although the reason for the precaution is not given. Obviously however, these terms are used in but a. comparative sense, to make plain that the operation 'is not one of roasting, and that the doors of the lithopone inutiles are kept closed as much as possible. In actual working the lithopone is shoveled into the fur- Serial No. 468,788.

nace, of course with the doors open; it is rabbled, again of course with the doors open 'to permit introduction oi the rabbling tool; and iinally it is raked out for quenching, yet again with the doors open. ln the sense of the present invention this is not working with exciusion ci? air; it cannot prevent the development ci the yellowish tint which'is characteristic ci a, lithopone that is oii color.

ln describing my invention in detail, shall first describe the illustrated furnace embodying it so far as it relates to appara tus, but although I describe the invention by reference to such illustrated apparatus it will be understood that l do not restrict. it thereto. lln the accompanying drawings of this furnace Figure 1 is a cross-sectional view substantially on the line 1--1 of Figure 9., looking in the direction of the arrows, with certain parts broken away to economize space;

Figure 2 is a top plan view to a somewhat smaller scale than .Figure l. and

Figure 3 is a top plan view of one of the air-excluding feeders.

The illustrated furnace comprises in gen` eral a fire box l having a suitable grate l, and a. latter includes, a hearth structure in the form of an upper hearth element 3 and a lower hearth element 4, domed partitions 5 anti 6 providing the annular chamber 7 in communication with the fire box Ti, by the passage 8 entering at 9, to directly receive the fiue gases therefrom, and the annular chamber 10 below the lower hearth element 4. The chamber 7 is connected with the chamber 10 by the lue 1l, and the chamber 10 is connected with the stack l2 by the iiue 13. A baffle wall 14 located between the entrance 9 and the iiue l1 closes thechamber 7, and a baille wall 15 closes the chamber l0 between the lues 11 and 13. `With this construction, the flue gases enter at 9, travel anti-clockwise (Fig. 2) around the chamber 7, pass down the fiue l1, travel anti-clockwise around the chamber 10, and pam into the stack 1Q at 13; thus the hearth structure is heated, the lower element 'to a higher temperature than the upper.

The Walls of the furnace structure are air-excluding. As here shown, the side walls are composed of steel e asbestos a, red brick calcining structure 2 or inuiile. The V and fire brick c, The top 17, partitions 5 and 6, walls 14 and 15, and bottom 18, are of fire brick. The hearth structure may be of any suitable material, as tile. To provide for the escape of steam from the wet raw lithopone, an escape pipe 40 is provided in the top 17; when Working there is suihcient excess pressure in the calcining structure to substantially ensure that no air will enter through the pipe. Desirably the hearth elements are supported by struts 5* and 18d.

In further accordance with the invention, a shaft 16, desirably hollow for cooling, is centrally and rotatably borne in the top 17 and bottom 18 in such manner as to exclude air, as by the close fitting bearings 17a and `18. This shaft carries two diametrically extending arms 19 and 20, one in each cham- 3 or 1. On cach arm is carried a series of plows or agitating devices 19a or 20a. Each plow is in the character of a vertical plate 21, connected with the related arm at 22. The plates are set with their vertical planes at an angle to the radii of the hearth element, the plates for the up r element being set to move the materia on the hearth radially inward, and those for the lower being set to move the material outward, as the shaft 16 rotates. The hearth elements are connected for the fall of material from the upper to the lower by the passage 23 formed by the upstanding circular eXtensions 5x1 and 6 of the partitions 5 and 6. With the construction outlined it will be seen that lithopone can be continuously moved through the furnace- (traveling gradually around and across the hearth elements) and while being thus moved through the furnace will be continuously stirred and agitated, the operation being carried on with exclusion of air, the access of air which is a necessary accompaniment of rahbling in the ordinary manner being eliminated.

In yet further accordance with the invention, means are provided for the feeding of the lithopone to the furnace, and the feeding of it from, i. e. discharging of it from, the furnace, with the exclusion of air. `As here illustrated such means comprises a feeder 24 at the top of the furnace and in communication with the hearth element 3,-

adjacent its periphery, by the passage 25, and a similar feeder or discharger 26 in communication with the periphery of the hearth element 4 by the downwardly sloping passage 27. Each device comprises a cylindrical casing 28 in which is axially and rotatably mounted a feeder proper 29 comprising a series of blades 30 radiating from the rotatable shaft 31. These blades are sufficient in number to provide that they shall at all times close the passage 25, or 27; the blades fit closely in the casing 28 and travel close to the walls thereof, and the device is tightly connected with the furnace walls. Thus the lithopone can be fed to and taken!rv from the furnace Without access of air.

Desirably the shaft 31 of each device is continuously driven, as by the Wheel 32 being connected to any suitable driving means as an electric motor (not shown.) The wheel 32 of each device is connected to the related shaft 31, preferably by reduction gearing 33. The central shaft 16 is continuously driven, as from an electric motor (not Shown) connected to the ,Wheel 34 geared with the lowerend of the shaft 16 by the reduction gearing 35, 36, 37, 38, 39.

The arrangement provides for the continuous calcination of lithopone sincel the material can be continuously fed in at the device 24, continuously moved acro the hearth 3 4, and continuously discharged through the device 26, and the entire calcining operation is performed Without access of air, as neither the feeders nor the stirrer appreciably permit air to enter the furnace,

The general method of carrying on the process with the aid of the furnace will be evident from the above description. As to certaindetails of operationz. the up er hearth element is preferably heated f) b radiation) to somewhat above 250 C. and the lower to about 550 C. to 750 C.; the shaft 16 is driven at a speed to provide that a given portion of the lithopone passing through the furnace will be raised to. and maintained at, a temperature ranging between 550o and 750o C. long enough (for eX- ample 1 hour at 650 C.) to impart the desired hiding power by the time said portion reaches the passage 27, and the devices 24 and 26 are driven at a speed to supply and remove .the lithopone at a rate to ensure continuous uninterrupted operation. The lithopone discharged at 26 is quenched in Water contained in the trough 41.

In applying the terms air excluding and the like to the various structures above mentioned, I mean to include structures which although not absolutely air tight yet eX- clude air to such an extent that the amount of air which does enter is insufiicient to render the lithopone off color, that is, insuficient to reduce the brightness or deepen the tint of the lithopone to an objectionable extent for paint purposes. For example, when calcining lithopone comprising a small amount of chlorides absolute exclusion of air is not essential. although such a degree of exclusion as will prevent discoloration, and by reason of thatcan properly be called air exclusion in contradistinction to the haphazard methods of the prior art, is essential; and a furnace which would exclude such air as would be hatmful when working with such chloride-containing lithopone, although perha s not excluding all air, would be airexclu ing and fall Within my invention, and the ealcining operation would be, to all intents and purposes,'carried on while preventing access of air.

If desired, a suitable baflie-wall-and-iue arrangement for conducting the gases from the chamber lOand around the space bey ers, and so on, as are desirable for convenience in controlling the temperature may be provided, also, although I have referred to the chambers, as 7, as receiving flue gases, of course as is usual in mufe furnaces combustion need not be confined to the fire box.

I claim 1. The process of mufiling lithopone which comprises agitating the lithopone during calcination thereof while preventing access of air thereto.

2. The process of muliling lithopone which comprises calcining lithopone at a temperature 'of .from about 600 to 700 C. while excluding air therefrom, and frequently stir ring said lithopone during calcination While maintaining said exclusion of air.

3. The process of muiling lithopone which comprises passing a stream of lithopone, while agitating the same, through a calcining zone from which air is excluded, and

lheating the lithopone passing through said zone to a temperature of from about 600 to 700 C.

4r. The process of making lithopone which comprises continuously passing a stream of lithopone first through a calcining zone maintained at a temperature of from about 600 to 700 @fand then into a quenching liquid.

5. The process of muiing crude lithopone which comprises continuously paing a stream of lithopone, while stirring the same to secure uniform heating thereof, through a zone maintained at a calcining temperature.

6. The process of muiing crude lithopone containing a small proportion of a chloride which com rises continuously passing a stream of said lithopone through a calcining zone maintained at a temperature suiiciently high to give the lithopone the desired strength while stirring the lithopone and while preventing access to the lithopone in l the calcining zone of air. in an amount Suthcient to cause' the resulting finished lithopone to be o? color.

7. The process of muming crude lithopone containing a chloride which wmprises continuously passing a stream of said lithopone through a calcining zone while preventing access to the lithopone in the calcining zone oair in an amount suflicient to reduce the brightness or deepen the tint of the lithopone to an objectionable extent for paint purposes.

8. A mulie furnace for calcining lithopone comprising a calcining structure of airexcluding character and including a hearth structure,fand agitating means having au air-excluding mounting in said calcining structure and associated with said hearth structure to agitato the lithopone thereon.

9. A muliie furnace for calcining lithopone comprising a calcining structure of airexcluding character and including a hearth structure, an air-excluding feeding device located to discharge lithopone upon said hearth structure, and an air-excluding discharging device located to discharge lithopone from said hearth structure.

10. A muiiie furnace for calcining lithopone comprising a calcining structure of airexcluding character and including a hearth structure, an air-excluding feedmg device located to discharge litho one upon said hearth structure, an air-ex uding discharging device located to discharge lithopone from said hearth structure, and movable transferring means having an air-excluding mounting in said calcium' structure and located in proximity to sai hearth structure for moving lithopone on said structure from adjacent saidfeeding device to said discharging device.

11. A muiile furnace for continuously calcining lithopone comprising a calcining structure of air-excluding character and including a hearth structure, a continuously operab e air-excludin feeding device located to discharge ithopone upon said hearth structure, a continuously operable air-excludin discharging device located to discharge lit opone from said hearth structure, eontinuousl operable movable transerrin means aving an air-excluding mounting in said calcining structure and ic cated in proximity to said hearth structure for moving lithopone on said structure from adjacent said feeding device to said dischar ing device and means for driving said two devices and said transferring means.

12.` A muie furnace for calcining lithopone comprising a calcining structure of air-excluding character and including hearth structure. presenting an upper and a lower hearth element and a passage therebetween for the fall of lithopone from the upper to the lower element, and movable transferring means havingan air-excluding mounting in said calcining structure and including provisions or moving lithopone across said upper hearth element and to said passage.

13. A muiile urnace for calcining lithopone comprising a calcining structure of airexcluding character and including a hearth' structure presenting an -upper and a lower ist the lower element, an air-excluding feeding device located to discharge lithopone upon said upper element and spaced from said passage, au air-excludin discharging device located to discharge lit iopone from said lower element and spaced from said passage, and movable transferring means having an airexcluding mounting in said calcining structure and including provisions for moving lit-hopone from ad]acent said feeding device across said upper element to said passage, and for moving lithopone from adjacent said passage across said lower element to said dischargmg device. e

14. A. mule furnace for calcining lithopone comprising a calcining structure of airexcluding character and including a hearth structure presenting an upper and a lower hearth element, each substantially circular,

and a central passagetherebetween for the 20 cluding discharging device located to receive 25 lithopone froml adjacent the periphery of the lower element, and transferring means comprising a rotatable shaft having an air-excluding mounting in said calcining structure and carrying devices for moving litliopones 30 around and radially inward on said upper lelement and around and radially outward upon said lower element, upon rotation of said shaft.

In testimony whereof I ax my signature.

HERMAN G. SCHANCHE. 

